The conversion of olefins over ZSM-5 type catalyst is known in the art and is the subject of many patents. A wide range of techniques have been disclosed leading to the improved production of gasoline, distillates and lubricant range hydrocarbons through catalyst modifications, unique process conditions and the like. For example, U.S. Pat. No. 4,227,992 and the patents therein are excellent examples of the prior art in connection with this general subject.
In U.S. Pat. No. 4,517,399 to Chester et al, olefins are oligomerized over ZSM-5 type zeolite catalyst to obtain high viscosity index lubricating oils wherein the improvement involves the use of large crystal size ZSM-5.
In U.S. Pat. No. 4,547,613 to Garwood et al., light olefins are converted into a high viscosity index lubricating oil by contacting at elevated pressure with ZSM-5 type catalyst that has been conditioned by treatment with a light hydrocarbon gas at low pressure and elevated temperature.
In U.S. Pat. No. 4,520,221 to Chen, a process is disclosed providing high yields of lubricating oils with substantially higher viscosity indices from the conversion of light olefins such as propylene using ZSM-5 catalyst. The results are achieved by removing the surface acidity of the catalyst by treatment with a bulky amine. U.S. Pat. No. 4,568,786 to Chen et al. discloses a continuous process for the conversion of olefins to heavier hydrocarbons containing a lubricant fraction of high viscosity index by cofeeding a surface deactivating agent such as a bulky amine.
Some work has been reported on the dealuminization of zeolites using chelating agents resulting in an apparent increase in acidic activity of Bronsted Acid type. EDTA has been reported as a useful chelating agent for increasing the silia to aluminia ratio in zeolite. This work is reported in part by G. T. Kerr in A.C.S. publication Advances In Chemistry Series, Number 121 (1973), which publication is incorporated herein by reference. Such partly dealuminized zeolite catalysts have been considered to possess improved activity as cracking catalysts.
In the instant invention it has been surprisingly discovered that high yields of high viscosity index lubricant range oils can be produced by polymerizing or oligomerizing light olefins in contact with a metallosilicate catalyst, such as ZSM-5, that has been extracted with a metal chelating agent.